1. Field of the Invention
The present invention relates to a damper clutch of an automatic transmission and more particularly to a method and apparatus for controlling a damper clutch of an automatic transmission to improve shifting quality.
2. Brief Description of the Related Art
In general, a torque converter included in an automatic transmission is positioned between a crank shaft and transmission to multiply torque generated by engine and convey it to an input shaft of the transmission. The torque converter has a damper clutch for direct connection between crank shaft of the engine and input shaft of the transmission to improve fuel consumption by making a progress in energy efficiency when power is transmitted from the crank shaft of the engine to the input shaft of the transmission. Conventionally, the damper clutch is changed to its direct connection state through as long a period of time as possible in consideration of a better fuel consumption.
Besides, the direct connection of the damper clutch as such is made by operational pressure controlled by a control unit of the auto transmission. Operational conditions for the direct connection of the damper clutch generally are limited as follows: the temperature of an automatic transmission oil (generally named ATF, hereinafter referred to as operational oil) is kept at a constant state of over 30xc2x0 C.; the shift is not set at a parking, neutral or rear range; the running state of a vehicle is within the operational range of shifting patterns; vehicle is not in the process of shifting operations; and the shift is at its over 3rd or 4th running speed range.
Accordingly, if a vehicle""s running speed range and openness of a throttle valve are over predetermined values and if the operational oil temperature rises over a predetermined level while the shift is set at its over 3rd or 4th running speed range, the damper clutch will operate to convey the driving force transmitted from an engine to an input shaft of the shift by direct connection, thereby improving its fuel consumption.
After the damper clutch is directly connected, the operational oil temperature rises over a predetermined level in a running vehicle. Typically, the operational oil temperature rises to about 80 through 100xc2x0 C. and gets to this normal temperature state. Within this normal temperature range, the most precise tuning operations may be made for shifting quality. Therefore, it is the most advantageous to keep the normal temperature range of operational oil at about 80 through 100xc2x0 C. for the best shifting quality.
Although there have been attempts to alleviate shifting impact generated at the time of shifting of a conventional automatic transmission, such as by changing the operational range of the damper clutch according to the degree of outside pressure at a vehicle""s running area and by compensating a reduction in the driving force conveyed from the engine to the transmission, there has been developed no technique to control the operations of a damper clutch in considering the operational oil temperature relative to outside air temperature.
If a vehicle is running in winter or in the area like northern Europe and northern America where the outside air temperature is very low, the operational oil temperature does not rise close to 80 through 100xc2x0 C., but keeps its normal state at a lower temperature even after direct connection of the damper clutch of the torque converter by satisfying all relevant conditions. This is because heat emitted from the torque converter to outside at a lower temperature is of great quantity.
For instance, as shown in FIG. 1, if a vehicle is running in winter or in the area like northern Europe and northern America where the outside air temperature is low, the operational oil temperature does not rise close to 80 through 100xc2x0 C. (illustrated with a solid line) but keeps its normal state at a lower degree of an abnormal temperature range (illustrated with a dot line), even after direct connection of the damper clutch of the torque converter by satisfying all its relevant conditions. Thus, in the area where the outside air temperature is relatively low, the operational oil temperature does not get to its normal state at the range of about 80 through 100xc2x0 C. due to the great amount of heat emitted from the torque converter, but gets to its normal state at a lower temperature range, thereby deteriorating shifting quality of the automatic transmission.
It is one object of the present invention to solve the aforementioned problem and provide a method for controlling a damper clutch of an automatic transmission that can perform a normal shifting quality by selecting a correction value according to an outside air temperature for direct connection of the damper clutch and delaying the direct connection of the damper clutch until the operational oil temperature rises by considering the correction value to thereby enable it to get to an appropriate degree of operational oil temperature, i.e., a normal state of operational oil.
Thus, according to the present invention, there is provided a method for controlling a damper clutch of an automatic transmission, which includes detecting the outside air temperature, correcting oil temperature to determine a point of time for a direct connection of the damper clutch according to the determined outside air temperature, and performing controlling operations for direct connection of the damper clutch with a requirement that the operational oil temperature reaches to the correction value. In a preferred embodiment, the step of determining the outside air temperature includes detecting the operational oil temperature at an initial start stage, obtaining a rate of increase in the operational oil temperature according to the amount of heat generation of a torque converter over a predetermined initial period of time, and estimating the outside air temperature with the increase rate in the operational oil temperature due to the amount of heat generation of the torque converter.
Also, correcting the direct connection temperature of the damper clutch may be made by using mapped data of various correction values experimentally estimated according to various outside air temperature ranges to enable the operational oil to get to its normal state within a predetermined range of temperature at the time of tuning the transmission.
According to an alternative embodiment of the invention for controlling a damper clutch in an automatic transmission, a controller controls a process of determining an outside air temperature in which the transmission is operating, determining a point for direct connection of the torque converter to the transmission based on the determined outside air temperature, and controlling the damper clutch for direction connection in accordance with said determined point. Preferably, the point for direct connection corresponds to a temperature of operating oil in the transmission. Further, the determining the outside air temperature may be based on sensing an operational oil temperature for the transmission at an initial start stage, determining an amount of heat generated by the torque converter over a predetermined initial time period, determining a rate of increase in the operational oil temperature of said predetermined time period based on the amount of heat generated, and estimating the outside air temperature based on the sensed oil temperature and the determined rate of increase of the oil temperature.
In a further alternative embodiment, the determining of a point for direct connection includes selecting an oil temperature correction value corresponding to a difference between a normal direct connection temperature and a direction connection temperature adjusted for the determined outside air temperature. Preferably, the correction value is selected from a predetermined data map of correction values corresponding to outside temperatures that has been experimentally determined.
In another embodiment of the invention, a power transmission system is provided, which includes a torque converter receiving power input, an automatic transmission providing power output and a damper clutch operatively connecting said torque converter and transmission and providing for direct connection therebetween. An operating oil temperature sensor communicates with the transmission and a controller. The controller receives oil temperature input from said sensor and operatively communicates with the damper clutch to control direct connection of the torque converter and automatic transmission. The controller may include one or more processors and include instructions for controlling the damper clutch. Such instructions may involve estimating outside air temperature based on sensed operating oil temperature and heat generated by the torque converter, determining an operating temperature for direction connection based on the estimated outside air temperature, and controlling the damper clutch to directly connect the torque converter and automatic transmission at the determined operating temperature for direct connection. In a preferred embodiment, the system also includes a solenoid valve operatively connected to the damper clutch to effectuate direction connection.